Atrial electrode catheters are necessary for pacemakers which stimulate the atrium (as in AV sequential pacemakers) or sense intra- arterial electrical activity (as in atrial synchronous pacemakers). Existing atrial electrode catheters suffer from various deficiencies (too large; difficult to introduce; do not remain in place; etc.). The development of a suitable electrode catheter will add to the armamentarium used to combat heart disease.